Pencil lead and method of making same



l 'atentecl Aug. 21, 1934 PENCIL LEAD nn METHOD F MAKING l sAME r HaroldGrossman, Newark, N. Lassignor of one half to The American lLead PencilCompany,

Hoboken, N. 5., a corp oration of New York, and one-half to EberhardFaber Pencil 00.,

Brooklyn, N. iii, a corporation of New York No Drawing. ApplicationNovember 25 1932;

Serial No. 644,270

8 Claims. (01.106-5).

This invention relates to the manufacture of pencil leads, crayons andsimilar products which are used for marking upon surfaces, and has forits object the improvement of such products and "5 the method ofpreparing them, and particularly the treatment of crystallized graphiteswhereby these materials may be reduced to a finely divided condition,thereby permitting'the manufacture of improved pencil leads and thelike10 therefrom.

In'the manufactureof black pencil leads and the preparation of graphitefor use in such leads and in crayons and similar products used formarking, it is essential that the constitu cuts of the mixture used bein a very finely divided condition, in order that the marking elementmay be smooth. The usual practice heretofore requires the selection ofthe materials clay and graphite for purity, and the use preferably of anamorphous variety of graphite. The clay is washed to remove as much sandas possible, and is dried. The graphite is ground and air floated toensure the desired fineness. The clay and graphite are then mixed in thedesired proportions with water, and the mixture is again ground. Thegrinding is an extremely tedious operation, and the quality of theproduct depends to a large extent upon the time devoted to grinding. Thetime must, in any event, be prolonged to ensure an homogeneous andsmooth-writing product. In the preparation of high grade products,grinding frequently consumes weeks. When the grinding is completed, themass is filter pressed to remove surplus moisture and is worked into thedesired shape and baked.

It is the object of the present invention primarily to avoid the tediousgrinding for prolonged periods, and especially to permit the use .ofcrystallized graphites in the manufacture of pencil leads, crayons andthe like.

When crystallized graphites are subjected to a grinding operation, thegraphite is broken down or fractured across the planes of cleavage, thusexposing a multitude of rough edges. Consequently, in the attempt toincrease the fineness of such graphite the proportion of smooth slidingsurfaces to the rougher fracture surfaces is reduced. The smooth-writingquality of the leads produced from such material is correspondinglylessened, so that a large part of the benefit which should be securedfrom the grinding is lost. Improvement of the quality of the leads bygrinding is limited, therefore, when crystallized graphites areemployed.

In carrying out the present invention, the

difficulty is avoided by subjecting the graphite to chemical'oxidationin which the graphite i's converted into graphitic acid. Upon reduction,the graphitic acid is converted into graphite in a colloidal condition.This colloidal graphite *-beno cause of its fineness, is admirablyadapted for use in the preparation or" pencil leads, crayons and thelike. It maybe combined withclay of suitable fineness or other materialspressedfinto leads and the like, and baked. The graphite can be added toclay or other-suitable fillers, with'ap prcpriate binders, such as gums,resins, -etc., similar to the practice followed in making colored leads.In this case, it is not necessary to bake the leads. The resultingproduct affords a smooth- {0, i writing element of a quality surpassingany obtainable by the simple grinding of the graphite in the mannerhereinbefore described.

For the purpose of the present invention, the graphite is treated withstrong oxidizing agents, '15 for example a mixture of concentratedsulphuric acid (H2804) and potassium permanganate (KMnOl). Other strongoxidizing agents such as the bichromates, perchromates, chromates,perchlorates and chlorates of the alkali metals inja'o concentratedsulphuric acid may be used. The treatment of graphite with any of theseoxidizing agents in the manner described produces graphite in the formof ultramicroscopic particles, that is to say, in a colloidal conditionwhich may be defined for the purpose of the invention as that conditionin which the product in the aqueous suspension passes completely throughthe pores of a standard filter paper or shows no sediment after it hasbeen permitted to stand for considerable periods.

Chemical oxidation of graphite in the manner described affords a productwhich is most favorable structurally for the manufacture of pencil leadsand similar marking elements. The 001- loidal graphite produced consistsof minute scales or flakes which are split from the raw material inplanes parallel to the plane of cleavage. Consequently, the productaffords a maximum of sliding surfaces. When the colloidal product is.100 mixed with clay or the like and baked, the resulting leads, becauseof the sliding surfaces of the graphite, provide a smooth-writingelement of uniform quality and consistency.

As hereinbefore noted, the invention is pari ticularly adapted for thetreatment of graphites, which have a distinctly crystallized structure,such as Ceylon graphites. Such materials may be subjected to the methodas herein described and thereby reduced to a colloidal condition. After0 production of satisfactory pencil leads in a shorterv time and withmaterial savings with respect to the initial cost and maintenance andthe space required for the complicated and bulky grinding machine.

The invention as herein described and claimed relates particularly tothe production of pencil leads and similar marking elements, andinvolves the application in this art of the chemical oxidation ofgraphites to reduce them to a colloidal condition, followed by admixtureof clay or other materials of suitable quality, the pressing of themixture into strands, and thefinal baking of the strands to providefinished leads. Various changes may be made in the details of theinvention without departing therefrom or sacrificing any of theadvantages thereof.

7 I claim:

l. The method of producing marking elements which consists in subjectinggraphite to chemical oxidation to reduce it to a colloidal condition,mixing clay therewith, pressing the mixture into strands and thenburning the strands.

pencils consisting 2. The method of manufacturing lead for pencilsconsisting in chemically converting crystalline graphite by oxidationinto a colloidal form, admixing with thecolloidal graphite clay and/ orother additions, pressing the mixture into strands and subsequentlyburning the strands.

3. The method of manufacturing lead for in chemically convertinggraphite byoxidation into a colloidal form, admixing clay and binderswith the colloidal graphite and pressing the mixture into strands.

4. Pencil leads manufactured by the process set forth in claim 1.

5'. Pencil leads manufactured by the process set forth in claim 2.

5. A pencil lead comprising crystalline graphite transformedby oxidationinto colloidal state so as to have a crystalline structure especiallyfit for pencil leads.

7. The method of making pencil leads, consisting in convertingcrystalline graphite by oxidation into colloidal state, mixing thecolloidal graphite ai -w are

